The invention concerns a sliding bearing composite material with a metallic support layer, a porous carrier layer disposed thereon, and a sliding layer on the basis of PTFE which forms a sliding surface for a sliding partner, wherein the sliding layer material forming the sliding layer also fills the pores of the carrier layer and comprises at least 60 percent by volume of PTFE and 10-25 percent by volume of zinc sulfide.
A sliding bearing composite material of this type is disclosed e.g. in EP 0 232 922 B1. This document, however, does not mention a minimum content of 60 percent by volume of PTFE. For some length of time, the Assignee has produced a sliding bearing composite material which consists of 75 percent by volume of PTFE and 25 percent by volume of ZnS. This patent document also mentions that 5 to 40 percent by volume of aramide fibers, carbon fibers, glass fibers may be additionally contained as fillers.
EP 0 708 892 B1 discloses a sliding bearing composite material which does not disclose all of the elements upon which the invention constitutes an improvement, whose sliding layer material comprises PTFE and 2 to 20 percent by volume of fibrillated aramide fibers. In addition to PTFE, the embodiments also comprise PPS, PFA or calcium fluoride in various portions. This document does not give any further information.
WO 99/45285 discloses a sliding bearing composite material which does not disclose all of the features upon which the invention constitutes an improvement, whose sliding layer material should comprise PTFE, 10 to 30 percent by volume of a metal fluoride, in particular calcium fluoride and 2 to 10% fibrillated aramide fibers and 2 to 10% of a meltable fluoropolymer, FEP, PFA or MFA, wherein FEP is preferred. A specific embodiment is disclosed comprising 4 percent by volume of aramide fibers, 7 percent by volume of FEP, 18 percent by volume of CaF, the rest being PTFE.
WO 99/01679 discloses a sliding bearing composite material whose sliding bearing material comprises at least 60 percent by volume of PTFE, 15 to 25 percent by volume of a metallic filler, preferably lead, and in particular 8 to 12 percent by volume of PVDF and 1 to 3 percent by volume of carbon fibers oriented in a preferred direction. The use of metallic fillers, in particular lead, has become increasingly unacceptable.
DE 693 27 377 T2 discloses a sliding bearing composite material with a metallic support layer and porous carrier layer and a sliding layer, wherein the main component of the sliding layer material is PTFE. Moreover, zinc oxide whisker and magnesium oxysulfate are provided to improve the poor wear resistance of PTFE. In accordance with one embodiment variant, zinc sulfide is mentioned in addition to a large number of other available components.
DE 33 43 697 A1 also discloses a sliding bearing composite material with support layer and carrier layer and a sliding layer whose sliding layer material comprises a mixture of the following components: 0.1 to 50 percent by volume selected from one or more of solid lubricants such as metallic lubricants with low melting point for example Pb, Sn or alloys thereof, metal oxides, metal sulfides, metal fluorides, graphite or the like, and with fibrous materials such as carbon fibers and ceramics such as SiC; the rest being substantially PTFE, wherein the total amount of components, excluding PTFE, is within a range of 0.2 to 70 percent by volume.
EP 0 232 922 B1 discloses a sliding bearing composite material with 60 percent by volume PTFE, 20 percent by volume of glass fibers and 20 percent by volume of ZnS. This document further mentions that a polymer matrix material may contain glass fibers, glass balls, carbon fibers, ceramic fibers and aramide fibers individually or collectively in an amount of between 5 and 40 percent by volume, preferably 10 to 25 percent by volume.
EP 0 632 209 B1 also discloses a sliding bearing composite material with support layer, carrier layer and sliding layer, wherein the sliding layer material consists of PTFE, 50 to 30 percent by volume of metallic filler and 5 to 40 percent by volume of PVDF. The metallic filler is lead or zinc sulfide. A specific composition comprises 70 percent by volume of PTFE, 10 percent by volume of PVDF and 20 percent by volume of lead.
In view of the above, it is the underlying purpose of the present invention to produce a sliding bearing composite material of the above-mentioned type which has high wear resistance and yet a low coefficient of friction.